A conventional plasma torch comprises a torch body, an electrode table, an electrode, an insulating cylindrical body, a swirler and a nozzle as the main component elements thereof, the plasma torch being constituted by simply fastening the outer surface of the electrode table to the nozzle in the above-described sequential order and by inserting the thus-fastened elements into the torch body. Another known example is constituted in such a manner that a cap is fitted to the outer surface of the leading portion of the plasma torch and thereby the same is protected. Another known example is constituted in such a manner that the insulating cylindrical body and the swirler are integrally molded (for example, see Japanese Patent Utility Model Laid-Open No. 63-19978). Since the conventional plasma torches have been respectively constituted in the above-described simple manner, they can easily be manufactured. However, there arises the following problems when they are used:
(1) The insulating cylindrical body can be broken.
(2) The contact part between the electrode table and the electrode can be melted.
The reason why the above-described problems take place will be specifically described with reference to a plasma torch shown in FIG. 5. When the plasma torch is used, its electrode 3, which is one of the consumables, must be exchanged on occasion. In a case where the electrode 3 is mounted, a cap 7 is screwed so as to cause the electrode 3 to be fitted to the outer surface of an electrode table 2 via an insulating cylindrical body 4 and a nozzle 6. At this time, the force applied to the cap 7 acts on an outer peripheral portion 42 of the insulating cylindrical body 4. However, an inner peripheral portion 41 of the insulating cylindrical body 4 gives the electrode 3 the insertion force. That is, shearing force is generated in the insulating cylindrical body 4. Since the insulating cylindrical body 4 is usually made of ceramic, it has a disadvantageous point in that it is too weak against an impact or an excessively large stress, though it has satisfactory heat resistance. Therefore, the insulating cylindrical body 4 will be gradually broken, causing the force with which the electrode 3 is brought into contact with the electrode 3 to be reduced. As a result, there arises a problem in that a defective electrical connection (that is, defective contact) takes place and thereby the contact part 3b can be melted.
The nozzle of the plasma torch is, as shown in FIG. 6, arranged in such a manner that a small hole 11 for jetting out plasma arcs is formed at the central portion of the substantially conical leading portion thereof. Furthermore, a swirler 5 for introducing an operating gas in the form of a swirling flow or an axial flow into a portion between the electrode 3 and the nozzle 6 is fitted within a hole formed in a cylindrical portion 62 so that the electrode 3 is held via the swirler 5 and the insulating body 4.
Since the electrode 3 and the nozzle 6 of the plasma torch consume whenever the plasma arc generates, they must be exchanged when they reach the limit in terms of the use. In this case, since the swirler 5 can be further used, it is again used after it has been removed from the consumed nozzle 6. However, as for the nozzle 6, only a small gap, to which the swirler 5 can be fastened while preventing looseness, is permitted to be present in the hole formed in the cylindrical portion of the nozzle 6 through the overall length thereof. Therefore, when the consumed nozzle 6 is decomposed, it takes too much time to complete an operation of removing the swirler 5 from the nozzle 6. Usually, although the electrode 3 and the insulating body 4 can easily be removed from the nozzle 6, the swirler 5 is left in the nozzle 6 in a state in which the same is fastened there.
When the nozzle 6 in the above-described state is turned upside down and a small shock is applied to it, the swirler 5 can sometimes be removed from the nozzle 6. However, the swirler 5 cannot always be removed if the cylindrical portion 62 of the nozzle 6 is deformed or small dust is caught at a space between the swirler 5 and the nozzle 6 during the removal movement of the swirler 5. In a case where the swirler 5 cannot be removed even if the shock is given to the nozzle 6, the nozzle 6 must be cut to take the swirler 5. Therefore, there arises a problem in that the above-described nozzle cutting work causes the work for assembling/disassembling the plasma torch to take too much time.
Accordingly, a first object of the present invention is to provide a plasma torch having an insulating cylindrical body which cannot be easily broken and having a contact part between the electrode table and the electrode which cannot easily be melted. Furthermore, a second object of the present invention is to provide such a plasma torch having an improved structure. A third object of the present invention is to provide a plasma torch having a swirler which can easily be removed from the nozzle at the time of disassembling the plasma torch.